1. Field of the Invention
The present invention relates to a magneto-resistance effect element, a thin film magnetic head, and the like, which are suitably used for a hard disk drive.
2. Description of the Related Art
Hard disk drives employ a thin-film magnetic head having a magneto-resistance effect element (MR element) for reading magnetic signals. In recent years, efforts have been made to design hard disk drives for higher recording densities, and accordingly there are growing demands for thin-film magnetic heads, particularly magneto-resistance effect elements, which satisfy higher-sensitivity and higher-output requirements.
A CIP-GMR (Current in Plane-Giant Magneto-resistance) element which is a giant magneto-resistance effect element having a nonmagnetic layer between ferromagnetic layers and passing a sensing current in parallel to a layer surface, has been conventionally developed as a reproducing element in a thin-film magnetic head. On the other hand, a magnetic head that uses a TMR (Tunnel Magneto-resistance) element which has an insulation layer instead of the nonmagnetic layer as an intermediate layer and which passes a sensing current perpendicular to a layer surface, has also been developed in order to achieve higher densification. Furthermore, a magnetic head that uses a CPP (Current Perpendicular to Plane)-GMR element which is a GMR element having a nonmagnetic layer as the intermediate layer and passing a sensing current perpendicular to the layer surface similar to the TMR element, has also been developed. CPP-GMR element has an advantage of having low resistance in comparison with the TMR element and having higher output in a narrower track width than the CIP-GMR element.
An ordinary GMR element is interposed between the upper shield layer and the lower shield layer which also function as electrode films respectively, and such a GMR element is also referred to as a spin valve film (SV film). The GMR element is in the cylindrical shape of a desired size, and has a structure interposing a non-magnetic spacer layer between a pinned layer which is a ferromagnetic layer in which the magnetization direction is fixed and a free layer which is a ferromagnetic layer in which the magnetization direction varies according to an external magnetic field. A pinned layer is provided on an antiferromagnetic layer, whereby the magnetization direction of the pinned layer is fixed. Recently, there has been developed a CPP-GMR element in which an exchange coupling force from antiferromagnetic layers is effectively increased in such a manner that a pinned layer is formed not into a single-layer constitution of ferromagnetic material but into a three-layer constitution (synthetic pinned layer) consisting of a ferromagnetic layer (inner layer)/a nonmagnetic metal layer (nonmagnetic intermediate layer)/a ferromagnetic layer (outer layer), thereby imparting strong exchange coupling between the two ferromagnetic layers.
A hard magnetic film (hard bias film) made of CoPt or CoCrPt is provided around the CPP-GMR element via an insulation film such as Al2O3. The hard bias film is a film which is positioned at the side of the CPP-GMR element in the track width direction in order to control the magnetic domain of a free layer. A cap layer and a buffer layer are provided in the upper and lower ends of the CPP-GMR element, respectively. Thus, the CPP-GMR element is constituted so as to be inserted between an upper shield layer and a lower shield layer.
As disclosed in Japanese Patent Application Laid-Open No. 2005-294453, a NiFe alloy layer or a CoFe alloy layer is conventionally used as the free layer of the CPP-GMR element.
In recent years, according to an increase in the recording density of a hard disk drive, miniaturization of the CPP-GMR element has been advanced, so that the size of the CPP-GMR element may become 0.1 μm×0.1 μm or less in the top view. Such reduction in the size of the planar shape causes the current density to be increased to about 10−7 (A/cm2) or more. When the current density is increased, there arises a problem that spin transfer torque is generated to suppress the output of the magneto-resistance effect element.